How do you use your iPhone as a usb key?
Solution 1:
I haven't tried it yet, but from this description, it looks like Air Sharing is what I want.
Solution 2:
Also try Dropbox which is useful even just on Macs no iOS devices. If file is put into a public share then you could see it on your PC as well not just his.
Solution 3:
Not 100% relevant to the OP, but given the prices of flash memory these days and the hurdles one has to jump through to transfer arbitrary data to/from iOS devices I wouldn't recommend it.
If the user instead wants to access/modify the data while it's on the device the practice makes sense, but otherwise it is much more convenient today to just have a USB thumbdrive handy.
(BTW: The app in question was indeed likely to be Air Sharing, an app that's been available almost as long as the SDK has.)